MIT engineers have created soft, 3D-printed structures whose movements can be controlled with a wave of a magnet, much like marionettes without the strings. The menagerie of structures that can be magnetically manipulated includes a smooth ring that wrinkles up, a long tube that squeezes shut, a sheet that folds itself, and a spider-like 'grabber' that can crawl, roll, jump, and snap together fast enough to catch a passing ball. It can even be directed to wrap itself around a small pill and carry it across a table.
The researchers fabricated each structure from a new type of 3D-printable ink that they infused with tiny magnetic particles. They fitted an electromagnet around the nozzle of a 3D printer, which caused the magnetic particles to swing into a single orientation as the ink was fed through the nozzle.
By controlling the magnetic orientation of individual sections in the structure, the researchers can produce structures and devices that can almost instantaneously shift into intricate formations, and even move about, as the various sections respond to an external magnetic field.
Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering and Department of Civil and Environmental Engineering, said the group’s technique may be used to fabricate magnetically controlled biomedical devices.
“We think in biomedicine this technique will find promising applications,” Zhao said. “For example, we could put a structure around a blood vessel to control the pumping of blood, or use a magnet to guide a device through the GI tract to take images, extract tissue samples, clear a blockage, or deliver certain drugs to a specific location. You can design, simulate, and then just print to achieve various functions.”
Zhao and his colleagues have published their results in the journal Nature. His co-authors include Yoonho Kim, Hyunwoo Yuk, and Ruike Zhao of MIT, and Shawn Chester of the New Jersey Institute of Technology.
The team’s magnetically activated structures fall under the general category of soft actuated devices — squishy, moldable materials that are designed to shape-shift or move about through a variety of mechanical means.
For instance, hydrogel devices swell when temperature or pH changes; shape-memory polymers and liquid crystal elastomers deform with sufficient stimuli such as heat or light; pneumatic and hydraulic devices can be actuated by air or water pumped into them; and dielectric elastomers stretch under electric voltages.
But hydrogels, shape-memory polymers, and liquid crystal elastomers are slow to respond, and change shape over the course of minutes to hours. Air- and water-driven devices require tubes that connect them to pumps, making them inefficient for remotely controlled applications. Dielectric elastomers require high voltages, usually above a thousand volts.
“There is no ideal candidate for a soft robot that can perform in an enclosed space like a human body, where you’d want to carry out certain tasks untethered,” Kim said. “That’s why we think there’s great promise in this idea of magnetic actuation, because it is fast, forceful, body-benign, and can be remotely controlled.”
Other groups have fabricated magnetically activated materials, though the movements they have achieved have been relatively simple. For the most part, researchers mix a polymer solution with magnetic beads, and pour the mixture into a mold. Once the material cures, they apply a magnetic field to uniformly magnetise the beads, before removing the structure from the mold.
“People have only made structures that elongate, shrink, or bend,” Yuk said. “The challenge is, how do you design a structure or robot that can perform much more complicated tasks?”
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Image credit: MIT.